1. Field of the Invention
This invention relates to a magnification changing device in an optical system, and in particular to a mechanism for the magnification changing optical system of a microscope.
2. Description of the Prior Art
In a microscope, there is known a magnification changing optical system disposed between a sample and an eyepiece optical system to enable a zooming operation to be accomplished. As an example, first and second movable lens groups movable in opposite directions along an optic axis are provided between an objective lens group and an imaging lens group fixedly disposed in a direction of the optic axis, whereby a magnification changing optical system can be constituted. Each of the movable lens groups is supported by respective lens cases fitted in the cylindrical housing of the microscope, and each of the lens cases is coupled to a driving mechasnim disposed along the optic axis, In order to maintain an accurate coincidence between an optic axis of each movable lens group and a observation optic axis of the microscope during a movement of the both lens groups, it is preferable that a fitted portion of each lens case in the housing have a sufficient length in a direction of the optic axis.
However, in the case of such a structure, as the magnification change ratio becomes greater and the magnifiation increases, a movement ranges of the first and second lens groups widen and as a result, where a length of the housing is constant, a length over which each lens case is fitted to the housing must unavoidably be shortened and as a result the lens cases become inclined with respect to the optic axis when they move. By the lens cases becoming inclined, a position of the imaging plane is moved. This tendency becomes more remarkable as the magnification increases, and a disorder of a right and a left optic axes occurs in a stereoscopic microscope or the like. Also, this inclination has adversely affected optical aberrations.